This invention relates generally to metal founding, and more particularly to an apparatus for casting molten metal in a continuous casting machine of the wheel-band type.
In a known type of continuous casting machine, molten metal is poured into a mold defined by a peripheral groove in a rotatable casting wheel cooperating with an endless metal band which engages the casting wheel periphery to close the groove. Proper positioning of the endless band over the casting wheel periphery is necessary to prevent the molten metal from leaking between the band and groove and solidifying on the cast bar as a fin which must be removed before the cast bar is subsequently worked.
In one type of prior art continuous casting machine of the aforementioned type, proper positioning of the band on the casting wheel is achieved by providing retaining flanges on the casting wheel circumference adjacent the peripheral groove. Such flanges, in addition to interfering with the efficient cooling of the endless band as it engages the casting wheel periphery, subject the band edges to severe wear and damage resulting in short band life and reduced operating efficiency.
In another type of prior art continuous casting machine, such as that disclosed in U.S. Pat. No. 3,318,367 issued to T. L. Bray and assigned to the assignee of the present invention, a plurality of band support wheels are arranged about the casting wheel for engaging and supporting the endless band during its travel about the casting wheel periphery. One of these band support wheels is provided with a band positioning apparatus which includes linear motion means for moving the band support wheel axially along a line parallel to the casting wheel axis and pivotal motion means for pivoting the axis of the band support wheel about a pivot point laterally displaced from the support wheel. By appropriate adjustment of the linear and pivotal motion means, the band support wheel may be oriented with respect to the casting wheel so that, as the endless band passes therebetween, the band will be maintained in a path properly positioned over the casting wheel groove with a minimum of twisting and stress on the band. While the band positioning apparatus disclosed in U.S. Pat. No. 3,318,367 has proven to be an effective means for providing proper band tracking on a continuous casting machine, such band positioning apparatus includes a relatively complex and expensive arrangement of elements for linearly adjusting the band support wheel with respect to the casting wheel.
With the advent of larger and more sophisticated continuous casting machines having substantially longer bands and a large number of wheels for supporting and tensioning the band, a single band positioning apparatus, such as that described in the aforementioned U.S. Pat. No. 3,318,367 has proved inadequate in providing proper band tracking without inducing undesirably great stresses in the band. Experience has shown that the number of band failures due to band tracking devices increases with the number of wheels over which the band must travel and with an increase in the length of the band. The greater number of wheels renders effective band tracking more difficult with a single band positioning apparatus, and the longer bands are subject to greater overall variations in width and thickness than is the case with shorter bands.
Moreover, inasmuch as the band positioning apparatus described in U.S. Pat. No. 3,318,367 requires axial movement of the band support wheel shaft and inner sleeve, axial thrust is transmitted to the threads of the single linear motion adjustment shaft, rather than to the ball and socket member which has a greater axial thrust load capacity than the threads of the adjustment shaft. A further disadvantage of this arrangement is that the lubrication of the ball and socket member is rendered more difficult because of its mounting within relatively movable sleeves.
In a typical arrangement of large present-day casting machines, a number of the wheels upon which the band travels, e.g. idler wheels, pressure wheels and band support and tension wheels, are mounted such that their axes are relatively movable toward and away from the casting wheel axis. Even if the wheels are initially in substantially perfect alignment, subsequent movement of the wheels during operation of the casting machine, uneven bearing and band wear, tolerances in the fabrication of the band and the like, cause the band to become misaligned to such an extent that a single band positioning apparatus cannot provide proper band tracking. To maintain the longer bands of such machines properly positioned, the single adjustable band support wheel must be pivoted through a relatively large arc, thus causing large differentials in tensile stress across the width of the band. Such large stress differentials ultimately will cause stress cracks in the band, particularly along the more highly tensed edge portion of the band.